A flat panel display possesses advantages of being ultra thin, power saved and radiation free and has been widely utilized. Present flat panel displays mainly comprise a LCD (Liquid Crystal Display) or an OLED (Organic Light Emitting Display).
To be compared with a well developed TFT-LCD, an OLED based on the Organic Light Emitting Diodes is an active light emitting display, which possesses outstanding properties of self-illumination, high contrast, wide view angle (up to 170°), fast response, high luminous efficiency, low operation voltage (3-10V), ultra-thin (thickness smaller than 2 mm) and etc. The display devices utilizing OLED technology has possibility to have a lighter, thinner, charming appearance, more excellent color display quality, wider view range and greater design flexibility. The more important thing is that the environmental suitability of the OLED is far superior to the liquid crystal display. The tolerant temperature range can be −40-85° C. and the OLED is lead free and does not pollute the environment. Therefore, the OLED display must have become the only choice of the display technology of next generation.
According to the driving modes, the OLED can be categorized as PM-OLED (Passive matrix OLED) and AM-OLED (Active matrix OLED).
During the manufacture of the AM-OLED, the manufacture of diode driving elements is one of the key skills. Because the oxide semiconductor has higher electron mobility and the oxide semiconductor process is considered to be much simple than that of low temperature poly silicon (LTPS) which is also more compatible with the amorphous silicon process and meets the requirement of the new generation production lines for wide applications.
Generally, the present TFT substrate structure of an AM-OLED comprises a substrate, a gate, a gate isolation layer, an oxide semiconductor layer, an etching stopper layer, a source/a drain, a protecting layer, a flat layer, a pixel electrode, a pixel definition layer, photo spacers and etc. In the manufacture procedures, the formation of each layer structure requires one photolithography process and each photolithography process comprises processes of film formation, lithography, etching, stripping and etc. The lithography process further comprises processes of photoresistor coating, exposure and development and each lithography process requires creating one mask. The process becomes verbose, the manufacture skill is complicated and the production efficiency is lower; the more amount of masks is required, the higher the production cost became; meanwhile, the more the processes are involved, and the accumulated yield issue gets more significant.